In US 2002/0102490 of Ito et al., a process for synthesizing 3-(bicyclo[2.2.1]hept-5-en-2-yl)-1,1,1-trifluoro-2-(trifluoromethyl)propan-2-ol by reaction of cyclopentadiene with 1,1,1 trifluoro-2-trifluoromethyl-4-penten-2-ol complex is described. The monomer mixture resulting from that synthesis has an endo/exo isomer ratio of 80/20. Ito et al. is silent on synthesizing 3-(bicyclo[2.2.1]hept-5-en-2-yl)-1,1,1-trifluoro-2-(trifluoromethyl)propan-2-ol which is rich in the exo isomer. Ito et al. further discloses polymerizing 3-(bicyclo[2.2.1]hept-5-en-2-yl)-1,1,1-trifluoro-2-(trifluoromethyl)propan-2-ol with fluorinated olefins. Ito et al in “Synthesis and evaluation of alicyclic backbone polymers for 193 nm lithography” ACS Symposium Series (1998), 706 Micro- and Nanopatterning Polymers 208-223, American Chemical Society, discloses that radical polymerization of 3-(bicyclo[2.2.1]hept-5-en-2-yl)-1,1,1-trifluoro-2-(trifluoromethyl)propan-2-ol in the absence of catalyst is in general a very slow process thus to achieve reasonable addition polymerization rates of substituted norbornenes, metal based catalysts have been employed. Ito et al. identified certain comonomers, such as SO2, which would increase the rate of polymerization. This very limited number of comonomers appear to enhance the rate of polymerization. However, the foregoing approaches have drawbacks. Metal based catalysts leave residues which are highly undesirable for use in short wavelength photolithographic applications; and, the use of comonomers, such as SO2, degrade the transparency of the polymer at 157 nm. According to the Ito et al. publication the presence of SO2 also decreases thermal stability of the polymer.
Polymers used in photoresist compositions must be highly transparent, highly free of contamination, particularly metallic contamination, must be processible according to the methods employed in the art, and, of course, must be cost effective. Because of the potential for even minute metallic residues to contaminate nano-scale circuitry, it is highly desirable to prepare polymers for use in photoresist compositions without resort to metal catalysis.